1. Field of Invention
The present invention relates to full-bridge inverter power supplies, particularly of a type that is capable of operating in two modes.
2. Prior Art
Various loads, such as magnetrons or fluorescent lamps, require some form of pre-conditioning (such as the heating of a thermionic catahode) prior to being able to operate properly as a load. When, as frequently is desirable to do, such a load is powered by way of being effectively parallel-connected with the tank capacitor of a high-Q resonant circuit that is series-excited by the voltage output of an inverter power supply, a problem arises: before the load is operative to absorb power, the high-Q resonant circuit is effectively unloaded and it therefore represents an effective short circuit across the inverter's voltage output. This not only causes an excessively large power drain from the inverter, but also causes excessively large-magnitude voltages to develop across the circuit elements of the resonant circuit.
One way of circumventing this problem is that of providing the requisite pre-conditioning power from a separate source of power, and to delay the turning-on of the inverter power supply until after the load is properly conditioned. However, this approach requires the use of an extra power supply, and is therefore not as cost-effective as might be desired.